1. Field of the Invention
The present invention relates to a rubber stopper for sealing. More particularly, it relates to a rubber stopper which is partially or wholly coated by a cured coating layer of a specific fluorine-containing elastomer.
2. Description of the Prior Arts
Recently, it has been discussed on impurities adhered on a rubber stopper for sealing especially a rubber stopper for pharmaceutical application such as for sealing an injection. The impurities may be certain impurities remained on the rubber stopper after washing it or certain impurities formed by contacting the rubber stopper with a chemical solution, which are formed by various phenomena. According to a scanning electron microscope observation of the surface of the rubber stopper after washing, at a magnification of about 10.sup.2 to 10.sup.3 times, concave portions and adhesion of solid impurities are found. They may cause to increase impurities in ageing. In the rubber, a curing accelerator, carbon black, zinc oxide, titanium oxide and sulfur are incorporated. During the sterilization of the rubber stopper or the contact with a chemical solution, it is difficult to prevent the migration of the additive or the filler on the surface of the rubber stopper or dissolution of the additive or the filler.
When the sterilization with hot water or steam or ethylene oxide gas is performed after equipment of the rubber stopper on a bottle for an injection, such impurities may not be eliminated even though the virus and bacterium (hereinafter virus) can be eliminated.
The rubber for the rubber stopper usually has high friction coefficient to cause difficulty for removing virus and impurities adhered on the surface of the rubber stopper. The rubber stoppers having the tacky surface are mutually adhered each other whereby it is difficult to prevent a trouble caused in the stopper closing operation or the sterilization. During the transportation and storage of the rubber stoppers, the tacky adhesion problem causes a trouble.
Chlorinated butyl rubber used for a rubber stoppers of a vial bottle is a chlorinated product of butyl rubber obtained by copolymerizing isobutylene as a major component with isoprene as a minor component whereby there is possibility to cause chemical reaction on the surface of the rubber stopper in the sterilization with ethylene-oxide. It has been proposed to coat the surface of the rubber stopper with various synthetic resin coatings or cured synthetic rubber coatings in order to overcome various disadvantages for the rubber stopper for sealing especially rubber stopper for pharmaceutical application such as for sealing an injection. The synthetic resin coating is formed by laminating a synthetic resin film on the surface of the rubber stopper coated with the binder or forming a synthetic resin film in one piece on the surface of the rubber stopper. Such process usually requires complicated operations or sometimes is not applicable depending upon the configuration of the rubber stopper. The adhesion strength is not high enough whereby it may be peeled off during the use. Moreover, the synthetic resin coating sometimes may diminish the function of the rubber stopper for sealing. As the cured synthetic rubber coating layer, a cured fluorinated rubber coating having excellent chemical resistance and heat resistance can be considered. The adhesion characteristic to various substrates is not satisfactory.
According to various studies, a coating of cured rubber having self-adhesion property of a copolymer of propylene, tetrafluoroethylene and glycidyl vinyl ether is chemically stable in various sterilization of the rubber stopper to satisfy certain requirements, however, the contamination of the impurities caused by leaching or dissolving the impurities can not be prevented.
Various studies have been made under the consideration of such problems. As a result, the following surprizing fact has been found. The graft copolymer obtained by a chemical reaction of reaction sites of both the segments of a polymer having epoxide group obtained by a copolymerization of glycidyl vinyl ether as the fluorine-containing polymeric segments and a polymer obtained by a copolymerization of a siloxane having amino group as the organopolysiloxane segments, is a fluorine-containing elastomer having excellent heat resistance, chemical resistance and freezing resistance and can be formed as a cured coating layer having excellent properties on the surface of the rubber stopper and can substantially prevent contamination of the impurities.
The specific cured coating layer has lubricating property to prevent the trouble of tacky adhesion.